Because whether there is a God or not, the universe per se cannot have a purpose in any anthropomorphic sense for which that term is usually employed. The universe is simply the collection of galaxies, stars, planets, comets, meteorites, and other solar system detritus, plus whatever dark matter and dark energy turn out to be. The universe is governed by laws of nature that themselves have no purpose other than what they inevitably dictate matter and energy to do. Stars, for example, convert hydrogen into helium, and they have no choice in the matter once they reach a certain size and temperature. Stars are not sitting around thinking “my purpose in life is to convert hydrogen into helium so I better get on with it.” Ditto everything else in the universe, including all living organisms, from C. elegans to H. sapiens.

Life began with the most basic purpose of all: survival and reproduction. For 3.5 billion years organisms have survived and reproduced in a lineal descent from the pre-Cambrian to us, an unbroken continuity that has endured countless terrestrial and extraterrestrial assaults and five mass extinctions (six if you count the one we may be causing). This fact alone imbues us with a sense of cosmic purpose. Add to it the innumerable evolutionary steps from bacteria to big brains, and the countless points along the journey in which our lineage could have easily been erased, and we arrive at the conclusion that we are a glorious contingency in the history of life. As Charles Darwin wrote in the penultimate paragraph of his 1859 masterpiece On the Origin of Species: “When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Silurian system was deposited, they seem to me to become ennobled.”

Humans have an evolved sense of purpose — a psychological desire to accomplish a goal — that developed out of behaviors that were selected for because they were good for the individual or for the group. Although cultures may differ on what behaviors are defined as purposeful, the desire to behave in purposeful ways is an evolved trait. Purpose is in our nature. With brains big enough to discover and define purpose in symbolic ways inconceivable to billions of preceding and co-existing species, humans stand apart as genuinely unique in our attention to purposeful behavior. Evolution gave us a purpose-driven life.

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Whether there is a God or not, all of these purposeful activities — and many more — stand as ends in themselves in the here-and-now, not as means to some other end in the hereafter. Purpose is not some prop on a momentary stage before an eternal tomorrow, where its ultimate meaning will be revealed to us. Purpose is created by us through the courage of our convictions and the honor of our actions.